1. Field of the Invention
This invention relates to an automatic transmission for motor vehicles.
2. Description of the Prior Art
There is known in the art an automatic transmission including a first shaft rotatably supported by the automatic transmission case and consisting of an input shaft coupled with the output shaft of the engine through a fluid joint or a friction clutch and an output shaft disposed coaxially in series with the input shaft and mounting thereon an output gear; a second shaft consisting of a long shaft rotatably supported by the automatic transmission case parallel with the first shaft and a short shaft rotatably mounted on the long shaft, one of the long and short shafts serving as an input shaft having an input gear connected to an output gear on the first shaft by direct meshing engagement therewith or through a chain or an idler gear while the other one serving as an output shaft having an output gear; a differential having a large drive gear connected to the output gear of the second shaft by direct meshing engagement therewith or through a chain or an idler gear; a first speed-changing planetary gear mechanism provided between the input and output shafts of the first shaft; and a second speed-changing planetary gear system provided between the input and output shafts of the first shaft. In this sort of automatic transmission, there has been a difficulty that the long shaft of the second shaft which transmits large torque is bent due to the bending stress which is imposed on the input and output gears, giving rise to a problem that the service life of bearings at various sliding parts is shortened by localized application of load. Especially in a case where the load point of the output gear of the second shaft, which transmits an increased torque upon deceleration, is located away from the bearing which supports the output gear of the second shaft, the long shaft is subjected to a greater bending moment and the life of the bearing is shortened to a considerable degree.